KXOK 630 in St. Louis, one of Todd Storz's stations was a Class 3. In the early and mid-1960s, KXOK had all the Baby Boomers, KMOX had their parents, and everyone else was fighting for scraps.
There was a discussion a few weeks ago in another of the forums here about the fairly solid showing KSD made up to the mid-1970s. KXOK was actually somewhat vulnerable, which was discovered when KSLQ(FM) came on the air in 1972 with its "Super Q" format and cleaned KXOK's clock. One contributor was the coverage problem that you mentioned; a KXOK null happened to be right where the metropolitan area was growing fastest. You could hear KXOK at night, but it was noisy.
KXOK (now KYFI) was not the original occupant of 630 in Missouri. KFRU in Columbia was. The St. Louis Star-Times bought KFRU in 1936. At the same time, it was building KXOK in St. Louis at 1250, which would have been 1280 after the 1941 frequency shifts. WIL and KSD opposed the construction of KXOK. Due to the need to resolve those regulatory maneuvers, KXOK didn't get on the air until September 1938.
KFRU had to share time with WGBF in Evansville, Indiana and until 1936, with a radio station operated by the state of Missouri in Jefferson City.
In 1939, KXOK applied for KFRU's frequency and proposed moving KFRU to a class IV channel, making what had been a regional station a strictly local station for Columbia. At the same time, KHOW in Denver applied to move from 920, which it had been sharing with KFEL, to 630. I've been told that the KXOK move made the KHOW move possible. The 1250 frequency went to WGBF, thereby giving it full-time operation. KFRU moved to 1370, now 1400. No doubt the FCC viewed these moves favorably, since they resolved two time-sharing situations, but Columbia got screwed in the process. I've never seen a report of the justification the Star-Times offered for these moves. Maybe I'll find one someday. It did seem as though the proposed move received little notice in Columbia.
After KXOK made its application, KSD, owned by a Star-Times competitor, the Post-Dispatch, entered its own application for 630 and proposed moving KXOK to 550. KSD was seeking to get out of its time-sharing arrangement with the Lutheran Church-Missouri Synod's KFUO. KFRU would still have been stuck with 1370 under this proposal. Finally, in 1940, the moves of KXOK, KFRU, and WGBF were approved, KFUO was moved to limited-time operation on 830 (now 850) and KSD was granted full-time status.
KXOK outlasted the Star-Times; KFRU was sold to a Columbia newspaper publisher and the Star-Times' station manager in 1948. I was KFRU's news director for four years in the 1980s; learning of KFRU's history, and the fact that it had much wider coverage before 1940, got me interested in the history of radio stations generally.